Balloon angioplasty procedures have been used in recent years with increasing success in the treatment of obstructed arteries, such as the coronary arteries. The procedure involves advancing a catheter having a special balloon at its distal end to the location of the stenosis. The balloon portion of the catheter is placed, in its deflated condition, in the stenosis and then is inflated under high pressure to compress radially and outwardly the biological material such as plaque which forms the stenosis. Balloon dilatation systems of this type are illustrated in U.S. Pat. Nos. 4,195,637 and 4,323,071. In those situations in which balloon angioplasty can be used, its successful use avoids the greater risk of complex and expensive bypass surgery.
Not all arterial stenoses are treatable by balloon angioplasty. Among the types of vascular obstructions which have not been treatable with the angioplasty technology are those in which the passage through the stenosis is so narrow that the balloon angioplasty catheter cannot be inserted into the stenosis, even when the balloon is in its collapsed, deflated condition. Thus, where the opening in a stenosis was only enough to permit passage of a guide wire, but not enough to permit passage of a deflated angioplasty balloon, the procedure could not be performed. In order to enable balloon angioplasty to be performed in such narrowly stenosed arteries, low profile dilatation catheters have been developed. The low profile dilatation catheters typically are capable of assuming relatively low cross sectional dimensions, particularly in the region of the balloon, so that when the balloon is deflated, it may be inserted, in that configuration, into a tight stenosis. Typically, such low profile dilatation catheters incorporate a fixed guidewire as an integral part of the catheter. The guidewire forms part of or extends through the catheter and facilitates manipulation of the catheter so that it can be steered through branches in the patient's vasculature. Among the significant advances in such low profile catheters is that disclosed in U.S. patent application Ser. No. 303,908 filed Jan. 30, 1989. The probe-like catheter described in application Ser. No. 303,908 is very small in diameter and has a small diameter thin walled balloon at its distal portion. The catheter is constructed and arranged to be advanceable through the patient's vascular system and can be controlled and manipulated from its proximal end so that it can be steered selectively at forks in the vascular system. The main body of the catheter includes a flexible elongate hollow main shaft adapted to transmit torque from a proximal to the distal end of the catheter. The smaller diameter balloon support wire is attached to and extends from the distal end of the flexible hollow shaft. A helical spring is mounted to the distal portion of the support wire. The dilatation balloon is attached at its proximal end to the distal portion of the main shaft and the distal end of the balloon is attached to the proximal end of the helical spring. An inflation/deflation port is formed in the hollow main shaft distally of the proximal balloon connection to communicate with the interior of the balloon for inflating and deflating the balloon. A distal segment of the catheter which projects beyond the balloon includes the helical spring and a portion of the support wire. The support wire is tapered within the helical spring to provide progressively increasing flexibility in a distal direction. The distal end of the distal segment is adapted to be bent to a curve and enables the catheter to be selectively directed and steered by rotating the catheter from its proximal end. The balloon is very thin. The diameter of the collapsed folded balloon portion of the catheter is very small and defines a very small profile.
In order to enable steering of the catheter, a distal portion of the catheter is formed from a highly radiopaque material so that it is readily observable under X-ray fluoroscopy. Typically, such catheters have included radiopaque elements in the distal segment of the catheter, distally beyond the balloon. Additionally, small radiopaque markers may be disposed at other locations along the catheter to enable fluoroscopic determination of the location of other portions of the catheter, such as the proximal end of the balloon. In the catheter described in aforementioned application Ser. No. 303,908, the helical spring in the distal segment of the catheter is formed from a highly radiopaque alloy so that it appears quite dark on the fluoroscopic screen. Although providing a highly radiopaque portion of the catheter distally of the balloon is important in positioning the catheter, it is relatively short and provides relatively little indication of the shape and configuration of the artery or arteries in which the catheter is disposed. The configuration of the patient's coronary anatomy is important to the physician. Typically, during an angioplasty procedure, the physician will cause a radiographic contrast liquid to be emitted into the arteries being treated that so for a brief interval, the contour and anatomy of the arteries may be observed. Often the physician also activates a camera to make a permanent, replayable recording of the coronary anatomy. The injection of radiopaque contrast liquid also enables the physician to examine and determine the location and nature of the stenosis or stenoses to be treated. Although it would be desirable for the physician to have a continuous fluoroscopic indication of the coronary anatomy, that cannot be done because it would require continuous infusion of radiopaque contrast liquid. The amount of radiopaque contrast liquid that can be infused into a patient is limited. Therefore, it is believed that there is a need for a means by which the coronary anatomy may be observed continuously but without requiring continuous use of radiopaque contrast liquid. It is among the objects of the invention to provide a balloon dilatation catheter which facilitates fluoroscopic observation of the coronary anatomy through which a substantial portion of the catheter is disposed.